Abstract
BACKGROUND: Long-Lasting Insecticidal Nets (LLINs) are effective malaria prevention tools. However, information is limited about their durability and wash resistance in field circumstances, especially in seasonal transmission areas in South Asia. This study comprised a systematic examination of usage, physical integrity and insecticidal activity of LLINs in households in Afghanistan, three years after distribution. METHODS: In 2014, 500 households in 5 malaria endemic Afghan provinces (Balkh, Herat, Khost, Kunduz and Nangarhar) that had received LLINs (PermaNet 2.0) three years earlier were randomly selected through cluster sampling. All household heads were interviewed about LLIN survivorship, usage and maintenance. One randomly selected LLIN from each household was rigorously inspected to calculate the proportionate Hole Index (pHI). Four location-specific pieces from 200 randomly selected LLINs (40 per province) underwent cone bioassay testing in the Jalalabad entomology laboratory, to measure mosquito knock-down after 60 min and 24-h mortality. The number and percentage of nets with ≥ 80% mosquito mortality was assessed. Five location-specific pieces from 34 randomly selected LLINs (5-8 per province) were tested for insecticidal content by High-Performance Liquid Chromatography (HPLC). RESULTS: Of the 1190 distributed LLINs, 1045 were still in the household at the time of the survey (survivorship 87.8%) and 1006 of those (96.3%) had been used every night in the past week. 9.1% of the LLINs were used by more than three people.. Physical integrity measurements indicated that 97.0% of the LLINs were in a serviceable condition (pHI 0-642), while 3.0% were 'too torn' (pHI > 642). Functional Net survival was 93.4% (95%CI 91.7-94.8%). However, only 28% of the LLINs met the WHOPES ≥ 80% mortality criterion. Washing of LLINs was associated with a significant reduction in mosquito mortality. Median deltamethrin concentration was 0.12 g/kg netting material (6.7% of the original concentration at production). CONCLUSIONS: LLIN survivorship and functional net survival in this setting was excellent, while only a minority of LLINs retained sufficient insecticidal activity after three years of usage. This study underlines the need for evaluation of real-life LLIN durability in field circumstances. LLIN washing should be avoided, as it lowers insecticide content and LLIN efficacy.